A 2016 Maserati Levante came into a workshop with the check engine light on and three competing O2 sensor codes: P2272, P0157, and P2198. The technician noted the illuminated warning light and connected their scanner to find Bank 2 reporting both a stuck rich condition upstream and a stuck lean condition downstream.
Sorting the sensor signals
The combination of P2272 for a lean condition and P0157 indicating low circuit voltage (under 0.1 V) on Bank 2 Sensor 2 points heavily to an internal sensor failure. When the post-cat sensor loses chemical activity or develops an internal short to ground in the signal circuit, the voltage drops. Our diagnostic engine ranked a defective rear oxygen sensor as the most likely cause at 75 percent. The verification steps are straightforward. You measure the signal voltage in real-time data with a warm engine. Then, disconnect the sensor to see if the scan tool registers the baseline reference voltage of around 450 mV.
However, the front sensor code complicates things. P2198 shows the pre-cat sensor (Bank 2 Sensor 1) is stuck rich. If this sensor is fouled or has a calibration fault, the engine control unit will pull fuel via negative short and long-term fuel trims. This forced lean condition can actually cause the rear sensor to legitimately report a lean mixture, triggering the P2272 code. To rule this out, you check the fuel adaptations for Bank 2 against Bank 1 and introduce a controlled vacuum leak to force a lean response.
Heat and wiring on the M156E V6
The M156E V6 twin-turbo engine generates extreme heat around the turbochargers and downpipes. This makes the wiring harness for the Bank 2 oxygen sensors highly vulnerable. Our platform ranked wiring or connector damage as the second most likely culprit at 55 percent.
Heat damage, chafing against the chassis, or corrosion in the connector can short the signal wire to ground. This forces the voltage near zero, setting P0157 and tricking the computer into seeing a constant lean mixture for P2272. Because the harness might share a ground or shielding with the front sensor, a single wiring fault can affect P2198 as well. Testing requires a visual inspection of the insulation, a short-to-ground measurement with the sensor unplugged, and verifying the 12V feed to the heater circuit.
The venturi effect in exhaust leaks
An exhaust leak upstream of the rear sensor, or near the turbo and catalyst flange, can pull in oxygen-rich ambient air. This venturi effect happens during exhaust pulses and causes the rear sensor to falsely read a lean mixture. Our engine gave this a 40 percent probability. You find this by smoke testing the exhaust from the tailpipes, applying soapy water to cold components under slight pressure, and looking for soot marks at the welds.
Review your own diagnostic data
If you see conflicting rich and lean codes on a single bank, look at the fuel trims before replacing the sensors. The diagnostic platform we build uses real repair data to structure these specific tests. Do you see similar heat-related wiring faults on twin-turbo setups in your bays? Reach out and let us know.